MedXFit—Effects of 6 months CrossFit® in sedentary and inactive employees: A prospective, controlled, longitudinal, intervention study

Abstract Background and Aims Sedentary behavior and physical inactivity are associated with musculoskeletal disorders (MSD). Muscle and mobility enhancing training is recommended to promote musculoskeletal fitness and prevent MSD. A functional fitness program emphasizing the importance of musculoskeletal fitness is provided by CrossFit®. However, data from long‐term CrossFit® interventions assessing measures of musculoskeletal fitness in sedentary and inactive individuals does not exist. Methods This prospective, controlled study investigates the effects of 6 months CrossFit® training (2×60 min/week) in inactive adults (in terms of <2 muscle or mobility enhancing training sessions per week) with predominantly sitting or standing occupations. 91 participants were initially assessed, 2 were excluded, 55 self‐selected for intervention (IG), and 34 for the control group (CG). Primary endpoint was a change in mobility (Functional Movement Screen score). Secondary endpoints were changed in strength (maximum isometric strength in kg; Dr. Wolff BackCheck®), and well‐being (WHO‐5 score). Key exploratory endpoints were changes in back‐issue measures (pain intensity, limitation, and frequency). Results 39 participants of IG and 31 of CG completed the evaluation after 6 months. The IG improved significantly more (p < 0.001) compared with the CG in the FMS (η² = 0.58), trunk extension (η² = 0.46), trunk flexion (η² = 0.47), trunk lateral flexion left (η² = 0.41), trunk lateral flexion right (η² = 0.42), upper body push (η² = 0.4), upper body pull (η² = 0.25), hip extension left (η² = 0.18), and hip extension right (η² = 0.4). Change of WHO‐5 scores did not significantly differ between groups (p = 0.55; η² = 0.01). Exploratory analysis of back‐issue data showed a higher decrease for pain intensity, limitation, and frequency in the IG compared with the CG. Conclusion This study proves for the first time within the scope of a prospective, controlled study the broad benefits of CrossFit® in inactive adults doing predominantly sedentary work.


| INTRODUCTION
Inadequate physical activity is considered as an important risk factor for chronic diseases like obesity, type 2 diabetes, cardiovascular diseases, and musculoskeletal disorders (MSD). 1,2 Modern working conditions play an important role regarding sedentary and inactive behavior. According to a nationwide German study (N = 18,026) 47.5% of women and 47.2% of men at the age of 18-64 stated to predominantly sit or stand during their working hours. The proportion increases with higher educational levels. 3 An active lifestyle and less sedentary behavior during leisure time could minimize negative effects. 4 However, another study (N = 22,959) states that only 42.6% of women and 48% of men at the age of ≥18 meet the minimum level of ≥ 150 min of moderate-intensity aerobic physical activity recommended by the WHO. 5 Muscle enhancing activity recommendations (≥2 workouts/week) are met by 27.6% of women and 31.2% of men. 6 As mentioned above this may support the development of several diseases. Especially MSD has to be mentioned here. In a study concerning the health status of adults 57.9% of women and 52.2% of men reported joint pain in the past 12 months. 7 Furthermore, MSD alone is responsible for about 25% of sick days, 2 are associated with a lower quality of life, and may accelerate the loss of functional capacity below the disability threshold. 8 Aside from that, an intact musculoskeletal system (strength, coordination, and flexibility) is the foundation to stay physically mobile and train other physiologically important systems (e.g., cardiopulmonary and nervous system). While strength, 9,10 coordination, 11 and flexibility 12 deteriorate with age, physical training has widely been proven to slow down this decline and keep the musculoskeletal system intact. 13 Based on those findings functional strength and conditioning programs embedded in corporate health management programs might help to keep the musculoskeletal system intact, hinder the development of noncommunicable diseases and reduce sick days in physically inactive employees doing predominantly sedentary work.
A time-efficient training system that covers the recommendations of the WHO and American College of Sports and Medicine to improve health is provided by CrossFit ® (CF). 4,5 CF is a high-intensity, functional fitness program. What stands out about CF is the integration of exercises from various disciplines such as weightlifting or gymnastics, which place high demands on strength, coordination, and mobility. 14 Scientific literature in this field covers the effects of CF on body composition, life and health aspects, psycho-physiological parameters, psycho-social behavior, and the risk for musculoskeletal injuries. 15 Positive effects of CF have been found in six fitness domains (cardiovascular/respiratory endurance, stamina, strength, flexibility, power, and balance). [16][17][18] Injuries in CF (3.1 injuries/1000 h of training) occur as often as in weightlifting, powerlifting, gymnastics, and fitness training but less often than in contact sports like rugby. 19 According to an online survey 19.4% of 386 CF athletes got injured in a 6-month period, with shoulder (25%) and low back injuries (14.3%) being the most common. 20 Nevertheless, only a few studies on CF with a high level of evidence and low risk of bias currently exist. 15 Data regarding long term effects of CF on the musculoskeletal system in populations that have an increased risk for developing noncommunicable diseases (e.g., MSD) have yet to be collected.
Therefore, the aim of this study was to investigate whether 6 months of CF training improve mobility (primary endpoint), strength (secondary endpoint), and well-being (secondary endpoint) in inactive individuals (in terms of <2 muscle and/or mobility enhancing training sessions per week prior study participation) with a predominantly sitting or standing occupation. Furthermore, back issues were assessed for exploratory purposes.

| Trial oversight
This study followed a prospective, longitudinal intervention design with control (CG) and intervention group (IG). Data were collected from October 2020 to August 2021. Both groups were tested in the same manner at baseline (t0) and after 6 months (t1) and self-selected for either IG or CG. Participants of the CG were instructed to maintain their current activity level. This was checked via question-

| Participants
Military and civilian personnel of the UniBw M (age = 18-65 years, male and female) was invited to participate in the study by flyer and email. Inclusion criteria were a predominantly sitting or standing occupation and inactivity in terms of participation in less than two muscle and/or two mobility enhancing training sessions per week. Exclusion criteria were pregnancy and health issues that would disqualify for participation in regular exercise and the applied tests (severe injuries to the musculoskeletal system, osteoporosis, intervertebral disc damage, joint replacements, hypertension, and fresh scars). Inclusion and exclusion criteria were checked via questionnaires at t0 and t1.
Demographics and anthropometrics of initially assessed participants are displayed in Table 1. When participants were not able to attend the test session t1 in the laboratory (e.g., sickness, remote work, and quarantine) surveys were done by telephone.

| Training intervention
CF is a strength and conditioning program that attempts to improve physical competence in 10  technical exercise execution to achieve high levels in safety, efficacy and efficiency. 14 The IG committed to attend two training sessions per week for 6 months. These were 60-min-group-sessions supervised by a coach.
Participants had to sign in for each session via online schedule.
Registrations were tracked.
The training format included 0-10 min introduction and warm-up,

| Endpoints and protocol
Primary endpoint of this study was the change in mobility (Functional Movement Screen score) 21 any issues in the past 6 months in the above-mentioned areas.
Thereafter, they were asked to rate their average pain intensity and limitations on an 11-point scale (0 = no pain or limitation, 10 = highest imaginable pain or limitation). Furthermore, pain frequency was assessed in days per week suffering from issues in the particular area.
For pain intensity, limitation, and frequency the area with the highest value was selected for the analysis.

| Statistical approach
This study included exclusively individuals that did less than two muscle and/or mobility enhancing training sessions per week prior the study. Consequently, low baseline FMS scores were expected.

| RESULTS
Of 91 participants initially screened, two did not meet the inclusion criteria as they already did more than two muscle-enhancing training sessions per week prior to intervention.

| Secondary endpoints
The IG had higher maximum isometric strength values for all tested movements at t0. For TLFr the difference was significant (p = 0.047). However, the difference for HEr was higher (η² = 0.4). Differences in change values between IG and CG are displayed in Figure 3.
Mean WHO-5 scores of the CG were higher at t0 compared to the IG but did not reach statistical significance (p = 0.26

| Exploratory endpoints
Regarding back issues there were no significant differences between groups at t0 for pain intensity scores (p = 0.75), limitation scores (p = 0.84), and pain frequency (p = 0.95). It is to mention that high proportions of both groups did not suffer from serious back issues at t0. As displayed in Figure 4, the number of pain-and limitation-free individuals increased in both groups after 6 months. and t1 as well as change within and between groups are shown in Table 3. Medians and interquartile ranges for back-issue data are provided in Table S5.

| DISCUSSION
The aim of the MedXFit study was to investigate the effects after 6 months of CF training on mobility, strength, and well-being in individuals with a predominantly standing or sitting occupation that did less than two muscle and/or mobility enhancing training sessions per week prior study participation. Additionally, back issues were assessed for exploratory purposes.
After 6 months significant effects were found for mobility and strength, but not for well-being.
F I G U R E 3 Strength: difference in change between groups from baseline (t0) to 6 months (t1 reported a score of 15.9 in CF-athletes with at least 1 year of training experience that did not attend any specific mobility program (MobilityWOD) before.
Strength gains after CF training were confirmed by previous studies. 15 Goins  However, comparison of this study with previous ones is difficult.
Most of them were short-term interventions with small sample sizes. Furthermore, they used complex compound movements (e.g., back squat, deadlift, and shoulder press) to measure strength. 30,31,[33][34][35] Some of these movements belong to the nine fundamental movements prescribed by CF that are trained frequently. 14 Therefore, strength gains could partly be explained by improvements in movement proficiency in these exercises, especially when executed by inexperienced individuals during shortterm interventions. In the current study, strength was assessed under standardized conditions with isometric strength tests. These physical tasks are not directly integral in CF and thus bias caused by motor learning is minimized. Although the BC is high enough in pre-/posttest reliability to be used in scientific research, 24 it is hypothesized that motor learning can explain 2%-11% of improvements in the BC. 36 Nevertheless, the difference in change between groups after 6 months in the current study supports the assumption that CF is highly effective to increase maximum isometric strength (minimum η² = 0.18, maximum η² = 0.47).
Several studies confirmed a positive association between physical activity and well-being. 37 CF claims to be a safe fitness program with a clear health aspect. 14  pre and during COVID-19 restrictions observed higher musculoskeletal pain and resulting disability levels (especially prevalence of pain in the lower back, neck, and thoracic spine) when public life was restricted. 42 It is to mention that back-issue data were highly skewed and a significant difference between groups was found exclusively for pain intensity. Thus, results should be interpreted as exploratory.
Because of the long-term interventional design, adherence to the training program was a major concern prior to this study. Eventually, dropout rates were lower than expected. Higher dropout in the IG (29%) compared with the CG (9%) is primarily explained by the fact, that the expense for the IG was higher.

ACKNOWLEDGMENTS
The authors would like to thank the study participants for volunteering. No funding was obtained for this study. Open Access funding enabled and organized by Projekt DEAL.

CONFLICTS OF INTEREST
The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute an endorsement by the American College of Sports Medicine. Professional relationships with companies or manufacturers who will benefit from the results of the present study do not exist. The authors declare that they have no conflict of interest.

TRANSPARENCY STATEMENT
Tom Brandt affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.

ETHICS STATEMENT
The study was conducted according to the guidelines of the